Fan assembly

ABSTRACT

A fan assembly that includes a housing having an inner peripheral wall defining a flow through opening, a stator located within the through opening and comprising an annular array of stationary blades provided along the inner peripheral wall, a rotor comprising a hub having a front wall supporting an outer peripheral wall having a forward balancing ring and an aft balancing ring, and an annular array of non-stationary blades extending from the outer peripheral wall, and strengthening ribs.

BACKGROUND OF THE INVENTION

Contemporary aircraft include fans used for various cooling purposes. Inthe current configuration, the size, shape, and rotational speed aresuch that high hoop stresses occur. Currently such contemporary fans arebeing removed from the aircraft regularly at very short intervals andreturned to the factory for inspection. If any anomalies are detected,then the impeller is replaced, which results in a lengthy and expensiveupkeep process.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, the invention relates to a fan assembly including ahousing having an inner peripheral wall defining a flow through opening,a stator located within the through opening, a rotor comprising a hubhaving a front wall supporting an outer peripheral wall having a forwardbalancing ring and an aft balancing ring, and an annular array ofnon-stationary blades extending from the outer peripheral wall. The hubis made of cast metal with a plurality of strengthening ribs locatedbetween the forward balancing ring and the aft balancing ring.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross-sectional view of a prior art fan assembly;

FIG. 2 is an enlarged view of a portion of the prior art fan assembly ofFIG. 1;

FIG. 3 is a perspective view of the result of stresses found duringnumerical analysis of the prior art fan assembly of FIG. 1;

FIG. 4 is a front view of a fan assembly according to an embodiment ofthe invention;

FIG. 5 is a cross-sectional view of a portion of the fan assembly ofFIG. 4; and

FIG. 6 is a perspective view of the result of stresses found duringnumerical analysis of the fan assembly of FIG. 4.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates a partial cross-sectional view of a portion of aprior art fan assembly 10, which has been shown partially crosssectioned. The fan assembly 10 may be a cooling fan for an aircraftengine or other aircraft application having a housing 12 and a rotor 24,which may be moveably mounted within the housing 12 and a cooling airstream may be generated by the rotor 24 during operation of the fanassembly 10. A stator 20 may be located within the housing 12 and mayinclude an annular array of stationary blades 22. The rotor 24 includesa hub 26 and an annular array of non-stationary blades 28 extending fromthe hub 26. Two spaced apart bearings 30 may be operably mounted to thestator 20. A shaft 32 may be rotatably supported by the bearings 30 forrotation about a rotational axis 34. The rotor 24 may be operablycoupled to the shaft 32 such that both the shaft 32 and rotor 24 may beco-rotated.

As may more clearly be seen in FIG. 2, the hub 26 includes a front wall40 and a side wall 42. The side wall 42 is thickened at two longitudinallocations forming a first balance ring 44 and a second balance ring 46.The fan assembly 10 is approximately 16 inches in diameter, made of acast metal such as cast aluminum alloy. The use of casting is mainlybased on cost-effectiveness and the casting goes through machiningprocesses to finished dimensions, including the diameter. Theconfiguration of the fan assembly 10 results in high hoop stresses thatmay be comparable to the yield strength of the cast aluminum alloy. Forexample, the result of numerical analysis run on the fan assembly 10 isshown in FIG. 3. The numerical analysis has been illustrated as avariety of portions 50-58 representing ranges of stresses found in thefan assembly 10 at a predetermined rotational speed of 8,000 rpm. Itwill be understood that this is merely for illustrative purposes andthat the stresses within each portion may not be uniform throughout. Theportions 50 represent 63 psi to 5019 psi, the portions 52 represent 5020psi to 7561 psi, the portions 54 represent 7562 psi to 15184 psi, theportions 56 represent 15185 psi to 22808 psi, and the portions 58represent 22809 psi to 30432 psi. As it can be seen the numericalanalysis shows maximum stress levels above 30,000 psi.

Referring now to FIG. 4, a portion of a fan assembly 100 according to anembodiment of the invention is illustrated. The fan assembly 100 issimilar to the prior art fan assembly 10. Therefore, like parts will beidentified with like numerals increased by 100, with it being understoodthat the description of the like parts of the fan assembly 10 applies tothe fan assembly 100, unless otherwise noted.

A housing 112 including an inner peripheral wall 114 defining a flowthrough opening 116 may be included in the fan assembly 100. A rotor 124may be moveably mounted within the housing 112 and a cooling air streammay be generated by the rotor 124 during operation of the fan assembly100.

Referring now to FIG. 5, a stator 120 may be located within the flowthrough opening 116 and may include an annular array of stationaryblades 122 provided along the inner peripheral wall 114. It is alsocontemplated that the stator 120 may form a portion of the housing 112.The stator may have a diameter of at least 14 inches. In the illustratedexample, it is contemplated that the stator has a diameter of at least16 inches. A rotor 124 is also illustrated and includes a hub 126 havinga front wall 140 supporting an outer peripheral wall 142 having aforward balancing ring 144 and an aft balancing ring 146 and an annulararray of non-stationary blades 128 extending from the outer peripheralwall 142. In the illustrated example, the flow of air is left to rightthrough the flow through opening 116. The front wall 140 may include acollar 148, with the front wall 140 extending between the collar 148 andthe outer peripheral wall 142. As illustrated, the front wall 140 mayhave a convex cross section between the collar 148 and the outerperipheral wall 142.

It is contemplated that the hub 126 is made of cast metal with aplurality of strengthening ribs 160 located between the forwardbalancing ring 144 and the aft balancing ring 146. The strengtheningribs 160 may extend between the forward balancing ring 144 and the aftbalancing ring 146 and have any suitable radial spacing. As illustrated,the strengthening ribs 160 may extend in a direction generally parallelto an axis of rotation 134 of the rotor 124. The strengthening ribs 160may reduce in cross sectional area in a direction from the forwardbalancing ring 144 to the aft balancing ring 146 or may maintain aconstant cross sectional area. If the strengthening ribs 160 do reducein cross sectional area, they may continuously reduce in cross sectionalarea in a direction from the forward balancing ring 144 to the aftbalancing ring 146. The strengthening ribs 160 may be sized and locatedin any manner suitable to reduce hoop stress in the outer peripheralwall 142. It is contemplated that the reduction of the hoop stress maybe at least 20% than that of a stator without the strengthening ribs ata predetermined rotational speed.

For example, FIG. 6 illustrates the result of stresses found duringnumerical analysis of the fan assembly 100 having the illustratedconfiguration of strengthening ribs 160. The numerical analysis has beenillustrated as a variety of portions 170-176 representing ranges ofstresses found in the fan assembly 100 at a predetermined rotationalspeed of 8,000 rpm. It is contemplated that during operation, the fanassembly 100 may be rotated at a predetermined rotational speed of atleast 7,000 rpm. Including that the predetermined rotational speed maybe at least 8,000 rpm. It will be understood that this is merely forillustrative purposes and that the stresses within each portion may notbe uniform throughout. The portions 170 represent 63 psi to 6870 psi,the portions 172 represent 6871 psi to 14425 psi, the portions 174represent 14426 psi to 18202 psi, and the portions 176 represent 18203psi to21980 psi. As it can be seen, the numerical analysis shows maximumstress levels less than 22,000 psi. In the illustrated example, thereduction of the hoop stress is at least 30%, this is a significantimprovement from the prior art fan assembly 10.

The embodiments described above provide for a variety of benefitsincluding that they have a high reliability and require lessmaintenance, including less preventative maintenance. The embodimentsdescribed above result in improved fan service life, which results incommercial advantages including reduced maintenance cost and reduceddown time of the aircraft on which the fan assembly is installed.Further, the embodiments of the invention may be implemented with aminor modification to the casting tool, and thus cost and timing impactswould be minimal Further still, the weight increase is estimated at amere 5 percent, which will not jeopardize weight specifications.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A fan assembly comprising: a housing having aninner peripheral wall defining a flow through opening; a stator locatedwithin the through opening and comprising an annular array of stationaryblades provided along the inner peripheral wall; a rotor comprising ahub having a front wall supporting an outer peripheral wall having aforward balancing ring and an aft balancing ring, and an annular arrayof non-stationary blades extending from the outer peripheral wall; andwherein the hub is made of cast metal with a plurality of strengtheningribs located between the forward balancing ring and the aft balancingring.
 2. The fan assembly of claim 1 wherein the strengthening ribsextend between the forward balancing ring and the aft balancing ring. 3.The fan assembly of claim 2 wherein the strengthening ribs extend in adirection generally parallel to an axis of rotation of the rotor.
 4. Thefan assembly of claim 3 wherein the strengthening ribs reduce in crosssectional area in a direction from the forward balancing ring to the aftbalancing ring.
 5. The fan assembly of claim 4 wherein the strengtheningribs continuously reduce in cross sectional area.
 6. The fan assembly ofclaim 5 wherein the front wall comprises a collar, with the front wallextending between the collar and the outer peripheral wall, and thefront wall having a convex cross section between the collar and theouter peripheral wall.
 7. The fan assembly of claim 1 wherein thestrengthening ribs extend in a direction generally parallel to an axisof rotation of the rotor.
 8. The fan assembly of claim 1 wherein thestrengthening ribs reduce in cross sectional area in a direction fromthe forward balancing ring to the aft balancing ring.
 9. The fanassembly of claim 8 wherein the strengthening ribs continuously reducein cross sectional area.
 10. The fan assembly of claim 1 wherein thefront wall comprises a collar, with the front wall extending between thecollar and the outer peripheral wall, and the front wall having a convexcross section between the collar and the outer peripheral wall.
 11. Thefan assembly of claim 1 wherein the strengthening ribs are sized andlocated to reduce hoop stress in the outer peripheral wall.
 12. The fanassembly of claim 11 wherein the reduction of the hoop stress is atleast 20% than a stator without the strengthening ribs at apredetermined rotational speed.
 13. The fan assembly of claim 12 whereinthe reduction of the hoop stress is at least 30%.
 14. The fan assemblyof claim 13 wherein the predetermined rotational speed is at least 7,000rpm.
 15. The fan assembly of claim 14 wherein the predeterminedrotational speed is at least 8,000 rpm.
 16. The fan assembly of claim 15wherein the stator has a diameter of at least 14 inches.
 17. The fanassembly of claim 16 wherein the stator has a diameter of at least 16inches.
 18. The fan assembly of claim 1 wherein the strengthening ribsmaintain a constant cross sectional area in a direction from the forwardbalancing ring to the aft balancing ring.